#!/usr/bin/env sh
# Copyright (c) Tailscale Inc & AUTHORS
# SPDX-License-Identifier: BSD-3-Clause
#
# gocross-wrapper.sh is a wrapper that can be aliased to 'go', which
# transparently builds gocross using a "bootstrap" Go toolchain, and
# then invokes gocross.

set -eu

if [ "${CI:-}" = "true" ]; then
    set -x
fi

repo_root="$(dirname $0)/../.."

toolchain="$HOME/.cache/tailscale-go"

if [ ! -d "$toolchain" ]; then
    mkdir -p "$HOME/.cache"

    # We need any Go toolchain to build gocross, but the toolchain also has to
    # be reasonably recent because we upgrade eagerly and gocross might not
    # build with Go N-1. So, if we have no cached tailscale toolchain at all,
    # fetch the initial one in shell. Once gocross is built, it'll manage
    # updates.
    read -r REV <$repo_root/go.toolchain.rev

    # This works for linux and darwin, which is sufficient
    # (we do not build tailscale-go for other targets).
    HOST_OS=$(uname -s | tr A-Z a-z)
    HOST_ARCH="$(uname -m)"
    if [ "$HOST_ARCH" = "aarch64" ]; then
        # Go uses the name "arm64".
        HOST_ARCH="arm64"
    elif [ "$HOST_ARCH" = "x86_64" ]; then
        # Go uses the name "amd64".
        HOST_ARCH="amd64"
    fi

    rm -rf "$toolchain" "$toolchain.extracted"
    curl -f -L -o "$toolchain.tar.gz" "https://github.com/tailscale/go/releases/download/build-${REV}/${HOST_OS}-${HOST_ARCH}.tar.gz"
    mkdir -p "$toolchain"
    (cd "$toolchain" && tar --strip-components=1 -xf "$toolchain.tar.gz")
    echo "$REV" >"$toolchain.extracted"
fi

# Binaries run with `gocross run` can reinvoke gocross, resulting in a
# potentially fancy build that invokes external linkers, might be
# cross-building for other targets, and so forth. In one hilarious
# case, cmd/cloner invokes go with GO111MODULE=off at some stage.
#
# Anyway, build gocross in a stripped down universe.
gocross_path="$repo_root/gocross"
gocross_ok=0
if [ -x "$gocross_path" ]; then
	gotver="$($gocross_path gocross-version 2>/dev/null || echo '')"
	wantver="$(git rev-parse HEAD)"
	if [ "$gotver" = "$wantver" ]; then
		gocross_ok=1
	fi
fi
if [ "$gocross_ok" = "0" ]; then
    (
        unset GOOS
        unset GOARCH
        unset GO111MODULE
        export CGO_ENABLED=0
        "$toolchain/bin/go" build -o "$gocross_path" tailscale.com/tool/gocross
    )
fi
exec "$gocross_path" "$@"